I see that combo box reads remote data, but there is no selected value in combo, no mather that the form have a correct value for this field.

And when I open combo box for the first time it reads once again the values from database ?!?

The first problem (not selected combo box value) is happening only the first time I create a tab. On the next tab which have a new form and a new combo box created, the correct combo value is selected. Anyway the second problem remain, when combo box is opened for the first time in tab it loads data again